It is widely regarded as the body's least useful organ, a block of intestinal tissue that often becomes inflamed and occasionally threatens to kill us.

But the appendix is getting a bad press, says US surgery expert Bill Parker. Far from being an organ of evil, it serves a very useful function – by acting as a safe house for beneficial bacteria in our bodies. In effect, the much-reviled organ is really a sanctuary for helpful microbes, explains Parker, an assistant professor of experimental surgery at Duke University medical centre, in Durham, North Carolina.

"My idea is that the appendix is a storehouse, a cultivation centre for the normal, beneficial bacteria that our gut needs," he says. "That safe house would be necessary and useful in the event that the main compartment of bacteria, the large bowel, got contaminated with some kind of infectious organism and got flushed out."

The appendix is not unique to Homo sapiens. The great apes, other primates, the opossum, the wombat and rabbits: all have appendices. And in each case, Parker argues that the appendix behaves in a similar manner: as a resupply centre for benign microbes.

A crucial part of Parker's theory rests on the importance of the bacteria found in our intestines. Our bodies are made up of around 10 trillion cells. However, we carry about 10 times as many microorganisms inside our bodies, and most of these are found in our gut. Their relationship with humans is symbiotic. The bacteria take some of our sources of energy, our food in other words, and in return they help to prevent the growth of harmful, pathogenic bacteria, and also produce vitamins and hormones. They are crucial to our wellbeing, in short.

"Periodically, bacteria get shed out of the appendix," says Parker. Bacteria from the appendix can then reinoculate the system, he adds. "They would reboot the system and help those good bacteria get growing again."

Parker first outlined his ideas about the appendix in 2007 and researchers have since been searching for evidence to support them. In the current issue of Scientific American, one group has now revealed that it has found intriguing evidence that suggests Parker may be correct. A team led by James Grendell, at Winthrop-University hospital on Long Island, studied 254 patients who had histories of gut infections caused by Clostridium difficile. The bacterium – C diff, as it is usually known by doctors – is a deadly pathogen that is often encountered in hospitals among patients who have been put on prolonged courses of antibiotics.

These powerful doses of antibiotics can badly deplete the benign bacteria in patients' guts. When this happens, C diff – which they pick up from infected items in a hospital or nursing home – can grow quickly and take over their gut. The patient will then suffer severe bouts of diarrhoea.

But if Parker's idea is right, individuals without an appendix should be more likely to have recurrences of C diff infections than those with one. The latter group's appendices would provide sources for replenishing their guts with benign bacteria that would hold the C diff at bay.

And that is precisely what Grendell's group found. They discovered that patients without an appendix were more than twice as likely to have a recurrence of C difficile infections. Recurrence in individuals with their appendix intact occurred in 18% of cases. Recurrence in those without their appendix occurred in 45% of cases.

Darwin suggested that the organ was used by ancient humans for digesting leaves but as people's diets changed it shrank and degraded to how we find it today. But Parker's work is a striking piece of support for the idea that the appendix – far from being a redundant evolutionary vestige – has a role to play inside our bodies. The work is not proof that Parker is right, but it does suggest the scientist is on to something. As he says: "From all the signals we're now getting from the scientific community, it looks like we may be right on target."

However, Parker stresses he does not believe that people should hesitate in having an appendix removed should it become badly infected. Modern medicines can today provide the protection that appendices supplied in our evolutionary past. "It's really important to say that even though the appendix has a function, if you have that pain in the lower-right quadrant, get it taken out," he says. "It's life-threatening if you don't get it taken out, and you really don't need it in this culture."